We propose to study functional interactions and biogenetic relations among the membranes of the intracellular compartments that constitute the secretory pathway (i.e., endoplasmic reticulum, Golgi complex, secretion granules and discharge front of the plasmalemma). As a prerequisite for this inquiry, we intend to improve cell fractionation procedures by using (whenever possible) specific ligands (instead of general physical properties) for isolating subcellular components. We also intend to reduce, by appropriate means, the molecular contamination of these components by proteins adsorbed to their surface. Membranes derived from cell fractions of interest will be solubilized and their proteins analyzed by polyacrylamide electrophoresis in the presence of detergent. Comparison of their electrophoretograms will provide information about the extent of compositional overlap among these membranes. Selected proteins will be extracted from the gels (or otherwise prepared) and used to produce antibodies, which will become principal tools in exploring membrane interactions during intracellular transport and biogenetic relations among cellular membranes. The cell types selected for investigation are: the hepatocyte (rat), the erythroblast (mouse), and the exocrine pancreatic cell (rat).